(1) Field of the Invention
This invention relates to a fluorine-containing protoporphyrin derivative and its salts which are useful as a diagnostic agent in the early detection of minute cancer.
(2) Description of the Background Art
Many reports have been published which indicate that porphyrins are prone to concentrate in cancerous tissues.
On the other hand, recent technical advances have made it possible to lase tissues in the living body by use of glass fibers. A so-called photodynamictherapy, an application of this technique, has now been attracting a lot of attention, where a subject is administered porphyrins which have a marked tendency to concentrate or accumulate in cancerous tissues, then subjected to laser light which is absorbed by the porphyrins and in turn the cancerous tissues are destroyed.
The principle of photodynamic therapy is that upon receiving laser beams, atoms constituting porphyrins are excited to produce activated oxygens which attack the cancerous cells to extinguish them. Since porphyrins concentrated or accumulated in the cancerous tissues emit red fluorescence upon receiving beams in the vicinity of 400 nm, they are expected to be useful in the cancer diagnosis as well as the cancer treatment. Today, active researches are being made on the diagnosis and treatment using hematoporphyrin derivatives. However, since the hematoporphyrin derivatives currently in use are a mixture of various porphyrin derivatives, they have potential problems to meet the medicinal purposes. Therefore, they have not yet been put into practical use.
Besides, in order to make the photodynamic therapy practical and further utilize it in cancer treatments, improvement is called for as to the following disadvantages. First, the diagnosis and the treatment are limited to the region where glass fibers can reach. Second, even though the cancerous region is reached by the fibers, laser irradiation is useful only on cancer in situ, and cannot reach deeper cancer tissues. In such case, no treatment nor diagnosis are possible by this method.
As mentioned above, it is considered that there are limitations in detecting cancers by the laser irradiation using porphyrins.
In the modern medical field, there are proposed a variety of surgical and internal treatments including radiotherapy to cure cancer diseases. It is said that if we can detect cancers in their early stages, the curing ratio should be greatly improved.
We cannot overemphasize the importance of the early detection of minute cancer including precancerous regions. The early diagnosis is one of the most important subject matters in the modern cancer treatments.
Meanwhile, diagnosis of various diseases by NMR (nuclear magnetic resonance) has recently received a lot of attention due to the advantage in that the internal organs of the living body can be observed as they are without being affected. Especially, being coupled with the recent rapid progress in the development of superconductive magnets, the NMR diagnosis is expected to be a future diagnosis of many diseases.
Presently, NMR has been used to detect .sup.1 H nuclei in the living body. However, since the nuclei of .sup.1 H are present in water which occupies most of the living body, no minute configurations other than gross shapes of internal organs can be observed, and therefore, the detection of minute cancer is thought to be impossible. As the nuclear species capable of detecting NMR spectrums, .sup.13 C, .sup.15 N, .sup.31 P, .sup.19 F, etc. may be mentioned other than .sup.1 H. Among these, .sup.13 C and .sup.31 P are thought to give almost the same resolution as .sup.1 H since they are also present in the living body.